In a joint appearance Wednesday with his Social Democrats' allies, the Greens, Steinbrueck also backed calls for a so-called European debt redemption fund, aimed at helping struggling countries pay off debt. Merkel's government has vehemently rejected that idea and all other proposals for pooling eurozone debt, saying it doesn't want a "transfer union."

Steinbrueck says Europe has long been a transfer union and Merkel has accelerated that process during the crisis by agreeing to bailouts for some countries.